Tuesday, November 15, 2005

A study released yesterday at an American Heart Association scientific conference reports that heart attack rates in Pueblo, Colorado dropped by 27% following the July 2003 implementation of a 100% smoke-free ordinance covering all workplaces, restaurants and bars in the city.

According to the study: "In the year and a half before Pueblo's smoke-free ordinance went into effect, 399 heart attack patients were admitted to the city's two primary hospitals. In the year and a half following enactment of the ordinance, the number of heart attack admissions dropped to 291, representing a 27 percent decrease."

In response to the release of this study, the Campaign for Tobacco-Free Kids informed the public, through a press release, that these data provide evidence that secondhand smoke is a cause of heart attacks:

"The results of these studies should not be a surprise in light of the overwhelming evidence that secondhand smoke poses serious, even life-threatening risks to health."

"The conclusions of these studies are reinforced by the scientific evidence about the impact of secondhand smoke on cardiovascular health. Other studies have found that exposure to secondhand smoke increases the risk of heart disease among non-smokers by as much as 60 percent and that as little as 30 minutes of exposure to secondhand smoke can trigger harmful cardiovascular changes, such as increased blood clotting, that increase the risk of a heart attack."

"The Pueblo study adds to the mountain of evidence that secondhand smoke poses a serious threat to human health."

The Rest of the Story

While the Pueblo study is important because it adds to the evidence that smoke-free laws may result in a decrease in heart attacks, it does not, in my opinion, add to the evidence that secondhand smoke is a cause of heart attacks.

I do not agree that these findings are not surprising "in light of the overwhelming evidence that secondhand smoke poses serious, even life-threatening risks to health," I don't think the conclusion of the study is necessarily "reinforced by the scientific evidence about the impact of secondhand smoke on cardiovascular health," and I don't agree that the study "adds to the mountain of evidence that secondhand smoke poses a serious threat to human health."

Why?

Because the study was unable to (or did not attempt to) determine whether the decrease in heart attacks was attributable to a decrease in secondhand smoke exposure among nonsmokers or to a decrease in cigarette consumption among active smokers (or some combination of the two).

The problem, revealed in the article about the study but not in the Campaign for Tobacco-Free Kids' press release, is that: "The study didn't distinguish between smokers and nonsmokers, but rather represented a combination of both smokers and those impacted by secondhand smoke."

In other words, one cannot conclude from the study that the reduction in heart attacks was due to reduced secondhand smoke exposure among bar and restaurant customers, as opposed to reduced smoking among smokers due to the implementation of the law. The effect of smoke-free laws on reducing cigarette consumption and promoting smoking cessation among smokers has been well-documented.

If I had to take an educated guess, I would guess that the bulk of the reduction in heart attacks was due to reduced levels of active smoking, rather than reduced secondhand smoke exposure. The reason for this guess is that it is difficult for me to imagine that the limited, acute exposure that nonsmoking customers experience while dining or drinking is sufficient to explain 27% of the heart attack burden in Pueblo.

While I believe that secondhand smoke exposure among bar and restaurant workers could be significant enough to cause a measurable increase in their heart attack rates, there are simply not enough of those workers in the city to explain a 27% decline in heart attacks.

The only explanation that I think makes most sense, in the absence of data that would allow one to draw an evidence-based conclusion, is that reductions in active smoking explain the observed effect. It is plausible, based on the extent of smoking in the population and the magnitude of the relationship between smoking and heart attacks, that reductions in smoking could cause a 27% drop in heart attacks in Pueblo, but I don't see the same magnitude reduction in heart attacks being plausible from a reduction in secondhand smoke exposure (unless there were evidence to support such a conclusion).

What I find interesting in the Campaign for Tobacco-Free Kids' response is that the scientific evidence does not seem to be an obstacle in promoting the Campaign's agenda. I actually agree with that agenda (at least as far as promoting smoke-free workplaces goes); however, I would not make a public statement attributing the cause of the observed study findings without what I believe to be adequate evidence to support such a statement.

For a more detailed discussion of my recent observation that the agenda seems to be driving the interpretation of the science in the anti-smoking movement, rather than the science driving the agenda, see my earlier post.

Lest anyone get other ideas, I should make it clear that I do believe that secondhand smoke is a substantial threat to the health of bar and restaurant workers and that policies to protect these workers by eliminating this exposure are warranted. It's just that I try to be careful about making sure that the evidence used to support these policies is sound scientific data from which solid scientific conclusions can be made.

I just don't see how a study which found a reduction in heart attacks that is most likely attributable to reductions in active smoking provides strong evidence for the health effects of secondhand smoke.

While I think this study is important because it documents a rather rapid reduction in heart attacks following implementation of a smoke-free law, the rest of the story suggests that it should not be used to tout the health hazards of secondhand smoke in the absence of data indicating that the reduction in heart attacks was attributable to reduced secondhand smoke exposure, rather than (or in addition to) reduced active smoking.

No comments:

About Me

Dr. Siegel is a Professor in the Department of Community Health Sciences, Boston University School of Public Health. He has 25 years of experience in the field of tobacco control. He previously spent two years working at the Office on Smoking and Health at CDC, where he conducted research on secondhand smoke and cigarette advertising. He has published nearly 70 papers related to tobacco. He testified in the landmark Engle lawsuit against the tobacco companies, which resulted in an unprecedented $145 billion verdict against the industry. He teaches social and behavioral sciences, mass communication and public health, and public health advocacy in the Masters of Public Health program.